Personalising an interface to the needs and preferences of a user often
incurs additional interaction steps. In this paper, we demonstrate a novel
method that enables the personalising of an interface without the need for
explicit calibration procedures, via a process we call self-calibration. A
second-order effect of self-calibration is that an outside observer cannot
easily infer what a user is trying to achieve because they cannot interpret the
user's actions. To explore this security angle, we developed IFTT-PIN (If This
Then PIN) as the first self-calibrating PIN-entry method. When using IFTT-PIN,
users are free to choose any button for any meaning without ever explicitly
communicating their choice to the machine. IFTT-PIN infers both the user's PIN
and their preferred button mapping at the same time. This paper presents the
concept, implementation, and interactive demonstrations of IFTT-PIN, as well as
an evaluation against shoulder surfing attacks. Our study (N=24) shows that by
adding self-calibration to an existing PIN entry method, IFTT-PIN statistically
significantly decreased PIN attack decoding rate by ca. 8.5 times (p=1.1e-9),
while only decreasing the PIN entry encoding rate by ca. 1.4 times (p=0.02),
leading to a positive security-usability trade-off. IFTT-PIN's entry rate
significantly improved 21 days after first exposure (p=3.6e-6) to the method,
suggesting self-calibrating interfaces are memorable despite using an initially
undefined user interface. Self-calibration methods might lead to novel
opportunities for interaction that are more inclusive and versatile, a
potentially interesting challenge for the community. A short introductory video
is available at this https URL

介绍了一种名为 IFTT-PIN 的自校准 PIN 码输入方法，通过自校准的方式，用户可以自由选择按钮含义，从而提高用户界面的安全性和可用性。实验证明，IFTT-PIN 可显著减少针对 PIN 码的攻击解码率。